Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$235.99	3.104%	$243.3151	$243.32	$243.30	$243.30
Purchase #2	$57.66	12.438%	$64.8318	$64.83	$64.85	$64.80
Purchase #3	$17.31	13.112%	$19.5797	$19.58	$19.60	$19.60
Purchase #4	$107.90	3.305%	$111.4661	$111.47	$111.45	$111.50
Purchase #5	$190.29	13.143%	$215.2998	$215.30	$215.30	$215.30
Purchase #6	$208.75	9.229%	$228.0155	$228.02	$228.00	$228.00
Purchase #7	$140.44	11.640%	$156.7872	$156.79	$156.80	$156.80
7 purchase totals =	$958.34		$1,039.2952	$1,039.31	$1,039.30	$1,039.30